The present invention relates to control of synchronous motors for driving in synchronism machines or mechanisms which are not mechanically interconnected, and particularly to such motors used to drive independent conveyors which are to be synchronized. It is sometimes desired to operate two machines in synchronism both as to speed and position, for example, when a first conveyor of articles must deliver the articles to a second conveyor, and the conveyors must be synchronized so that the first conveyor delivers each article at a convenient position such as into a holder on the second conveyor. Where each of two conveyors is driven by separate respective drive motor to which it is geared, the relative positions of the conveyors can be controlled by controlling the respective drive motors. The various systems of the prior art for accomplishing position synchronism include systems in which one of the synchronous drive motors is dropped back by slipping past one or more field pole positions of the motor while the motors are running. In another system a separate static inverter is employed to drive each motor and the output frequency of one of the static inverters is temporarily increased or decreased to enable its machine to gain on or to fall back to the other machine. These prior art techniques illustrate the nature of the problem solved by the present invention.